Reference may be made to the following U.S. Patents of interest: U.S. Pat. Nos. 3,748,044; 3,817,425; 3,900,289; 3,682,305; 3,915,651; 4,042,338; 3,137,172; 3,759,667; and 3,805,998.
Many systems currently exist for automatically performing chemical analysis of blood samples or other organic liquids. Typically, such systems, as shown for example in the aforementioned U.S. Pat. No. 3,748,044, assigned to the same assignee herein, include instrumentation for automatically processing a multiplicity of individual samples by sequentially transferring through a pipet a portion of the individual samples, suitably mixing a reagent, if desired or necessary, and placing the mixture into a respective cuvette. Each of the transferred specimens may then be automatically analyzed by measuring a desired characteristic and the respective measurements presented on visual displays or printed on a recording tape.
It is, of course, desirable to increase the system throughput if possible, i.e., the number of samples which can be processed and measured per unit time, without degrading the instruments' accuracy of measurement. In some systems, care must be taken during loading of the individual, multiple samples to insure that the liquid level in each sample container is the same with respect to a reference level associated with the lower most position of the pipet probe. Since the pipet probe must sequentially enter each of the individual specimens, in such systems, individually setting the level of each sample insures that the pipet probe will only penetrate a minimum distance into the samples. This requires the time-consuming task of manually adjusting the level in each individual sample container, or providing a special mounting in the instrument for each individual sample so that the vertical positions of each sample can be adjusted. In either event, the prior art sample loading procedure is time-consuming or involves additional costly mounting apparatus in order to achieve the accuracy desired. It is to be understood, of course, that failure to control the amount of probe penetration into the respective samples leads to undesired sample carryover, the contamination of samples, and thereby significantly reduces the instrumentation accuracy attainable.
In addition to the minimum probe penetration to guarantee instrumentation accuracy, it is, of course, desired to minimize serum adhesion to the probe in order to increase the instrument's precision of measurement. Furthermore, it has been found that the prior art probe tip structures have a tendency to trap an air bubble at the tip which upon removal of the tip from the sample withdraws a sample bubble. This reduces the desired concentration of sample and thereby adversely affects the measuring accuracy. In addition, it was found that increasing the probe moving speed leads to a hammering effect which tended to undesirably drive reagent from the probe into the sample cup.